Wireless communication tag and wireless communication system

ABSTRACT

A wireless communication tag according to the present invention includes a first antenna  8  previously set with predetermined identification information, and for wirelessly communicating various types of data with a reader/writer  6 ; a controller (IC chip  14 ) for controlling the data communicated through the first antenna; a second antenna  10  for receiving an electromotive radio wave  4   e  for causing electric power by a radio wave; and a charging unit (rectifying circuit  16  and a capacitor  18 ) for causing electric power by the electromotive radio wave received from the second antenna as well as for storing the caused electric power. With use of the electric power stored in the charging unit, the first antenna supplies data relating to the identification information to the reader/writer. The second antenna also can provide the reader/writer with the identification information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of Japanese Patent Application No.2007-270097 filed on Oct. 17, 2007. The contents of this application areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication tag, whichmakes wireless communication with a reader/writer, and a wirelesscommunication system using the wireless communication tag.

2. Description of the Related Art

Conventionally, a communication tag using an RFID tag, for example, isroughly divided into two types, i.e., an active type and a passive type,in view of the associated communication system. For the active type, abattery is loaded as a power supply source for activating the wirelesscommunication tag. On the other hand, for the passive type, power isexternally supplied for activating the wireless communication tag. Theactive-type communication tag is not only costly, but also requiresbattery discarding or replacement at cycle of several years because thebattery must be loaded. On the other hand, the passive-typecommunication tag can achieve low cost and extended service life, andtherefore, its expanded use is anticipated.

Three communication systems of the passive type are available which arerepresented by an electromagnetic coupling system, an electromagneticinduction system, and a radio wave system. These three systems areselectively used depending on a frequency for use. For example, awireless communication tag 1 of the radio wave system is generallyconfigured to have an RFIDIC chip 3 and a transmitting and receivingantenna 5, as shown in FIG. 2, and performs radio communication with areader/writer (not shown). For example, a UHF band or a microwave bandis utilized as a radio wave frequency band. Furthermore, a dipolarantenna 5 which forms an entire length of a half wavelength (λ/2) of aradio wave, for example, is utilized as the transmitting and receivingantenna 5.

In this case, the wireless communication tag 1 of the passive type ischarged by receiving through the dipolar antenna 5 a radio wave (areadout radio wave) transmitted from the reader/writer. While thereceived radio wave is employed as power supply, the wirelesscommunication tag 1 activates the IC chip 3, thereby communicating theID (identification information) stored in the IC chip 3 to thereader/writer.

With the conventional wireless communication tag of the passive type asdescribed above, a communication distance is undesirably limitedaccording to the amount of power charge when the tag communicates the ID(identification information) with the reader/writer. Therefore, it hasbeen necessary for this wireless communication tag to continuouslyreceive a radio wave (a readout radio wave) transmitted from thereader/writer until an amount of power charge sufficient to makecommunication is obtained. Further, it has been necessary to ensure anelectric field with enough intensity required for power charge. In viewof the circumstances described above, Japanese Laid-open PatentPublication No. 2007-34951 proposes art of always supplying power foractivating the wireless communication tag from a commercially availablepower supply, thereby ensuring the sufficient amount of power chargeanytime and increasing a communication distance between thereader/writer and the wireless communication tag.

In the above-described art proposed in Japanese Laid-open PatentPublication No. 2007-34951, however, a configuration for connecting thecommercially available power source must be additionally set up, thusresulting in a complicated wireless communication tag structure and highmanufacturing cost. Furthermore, with this art, a condition for usingthe wireless communication tag is limited under an environment where thecommercially available power source can be ensured, so that a certainlimitation is undesirably imposed on an environment of using thiswireless communication tag.

The present invention has been made in order to solve theabove-described problems. It is an object of the present invention toprovide a low-cost wireless communication tag and a wirelesscommunication system, that ensure the sufficient amount of power chargeregardless of a use environment to thereby increase a communicationdistance with the reader/writer.

SUMMARY OF THE INVENTION

A first aspect of the present invention is directed to a wirelesscommunication tag previously set with predetermined identificationinformation. The wireless communication tag includes: (i) a firstantenna for wirelessly communicating various types of data with areader/writer; (ii) a controller for controlling the data communicatedthrough the first antenna; (iii) a second antenna for receiving anelectromotive radio wave for generating electric power by a radio wave;and (iv) a charging unit for causing electric power by the electromotiveradio wave received from the second antenna as well as for storing thecaused electric power. The electric power stored in the charging unit isused, thereby allowing either one of the first and second antennas toprovide, to the reader/writer, data relating to the identificationinformation.

According to the first aspect of the present invention, an electricpower is caused at very low cost and the thus caused electricity can besufficiently stored in the charging unit, by forming an antenna (thesecond antenna) that receives the electromotive radio wave to cause theelectric power by the radio wave, separately from an antenna (the firstantenna) that wirelessly communicates the data relating to thepredetermined identification information (for example, RFID) with thereader/writer. Therefore, the sufficient charging amount can be ensuredregardless of use environment, thereby making it possible to use thethus stored electricity at the time of providing the reader/writer withthe data relating to the identification information, so that stabletelecommunication can be performed (specifically, a communicationdistance between the wireless communication tag and the reader/writercan be lengthened).

A second aspect of the present invention is directed to a wirelesscommunication tag constituted as set forth below. In the second aspect,the second antenna wirelessly transmits the data relating to theidentification data to the reader/writer when the first antennawirelessly receives the data from the reader/writer.

According to the second aspect of the present invention, transmissionand reception of the data relating to the identification information canbe performed by purpose-built antennas, respectively. Specifically, thedata can be received by the first antenna and transmitted by the secondantenna, so that the data can be transmitted and received efficiently.

A third aspect of the present invention is directed to a wirelesscommunication tag as set forth below. In the third aspect, a radio wavefrequency (for example, a UHF band (band between 860 and 960 MHz) at thetime of communication between the first antenna and the reader/writer,and a frequency (for example, a band of 13.56 MHZ or 2.45 GHz) of theelectromotive radio wave received from the second antenna are setdifferent from each other.

According to the third aspect of the present invention, frequencyaccuracy, stability, modulation, and the like of the electromotive radiowave received by the second antenna can be set completely independentlyfrom the radio wave transmitted from the reader/writer and received bythe first antenna. In this manner, the first and second antennas can beprevented from interfering with each other in the case of using radiowaves of the same frequency. At the same time, the output frequency ofthe electromotive radio wave, for example, can be set within a frequencyband in which the radio wave output is under loose regulation. As aresult, the electromotive radio wave is transmitted on the conditionthat output thereof is increased, so that the wireless communication tag2 can be improved in the electromotive efficiency and the chargingefficiency.

A fourth aspect of the present invention is directed to a wirelesscommunication tag as set forth below. In the fourth aspect, a memoryunit for previously storing the identification information as well asfor storing the data controlled by the controller.

According to the fourth aspect of the present invention, a freedomdegree of capacity design for storing the data is increased realize thewireless communication tag capable of communicating the large volumetricdata.

A fifth aspect of the present invention is directed to a wirelesscommunication tag as set forth below. In the fifth aspect, the chargingunit includes a rectifying circuit and a secondary battery unit (such asa lithium battery or a capacitor). The secondary battery unit storeselectromotive force rectified by the rectifying circuit upon receipt ofthe electromotive radio wave from the second antenna.

According to the fifth aspect of the present invention, the wirelesscommunication tag according to the first aspect can be charged withelectricity upon converting alternating voltage into direct voltage.

A sixth aspect of the present invention is directed to a wirelesscommunication tag as set forth below. In the sixth aspect, therectifying circuit is formed as a bridge circuit.

According to the sixth aspect of the present invention, the aboverectifying circuit can be readily formed.

A seventh aspect of the present invention is directed to a wirelesscommunication tag as set forth below. In the seventh aspect, thewireless communication tag further includes a resonant circuit.

According to the seventh aspect of the present invention, formation ofthe simply constructible resonant circuit allows the tag to cause theelectric power thereinside by the resonance thereinside, thus achievinglow-cost production and ensuring the sufficient amount of power chargeregardless of use environment.

An eighth aspect of the present invention is directed to a wirelesscommunication tag as set forth below. In the eighth aspect, the secondantenna is configured of a resonant circuit.

According to the eighth aspect of the present invention, formation ofthe simply constructible resonant circuit allows the tag to cause theelectric power thereinside by the resonance thereinside, thus achievinglow-cost production and ensuring the sufficient charging amountregardless of the use environment.

A ninth aspect of the present invention is directed to a wirelesscommunication tag, including: (i) an IC device for storing predeterminedidentification information; (ii) a first antenna for receiving from anexternal reader/writer, a first radio wave including a reading-commandsignal, and for transmitting to the external reader/writer, thepredetermined identification information stored in the IC device andread out by the reading-command signal; (iii) a second antenna forreceiving a second electromotive radio wave from an externalpredetermined device; and (iv) a charging unit for storing electricpower caused by the second radio wave received from the second antenna.The wireless communication tag, in the case where the first radio wavereceived from the first antenna is strong, activates the IC device witha current caused by the received strong first radio wave, and reads outthe predetermined identification information stored in the IC device, bythe command signal included in the first radio wave. The wirelesscommunication tag, in the case where the first radio wave received fromthe first antenna is weak, activates the IC device with a resultantcurrent of a current caused by the received weak first radio wave and acurrent from the charging unit previously storing the electric power,and reads out the predetermined identification information stored in theIC device, by the command signal included in the first radio wave. Thewireless communication tag transmits through the first antenna to theexternal reader/writer, the predetermined identification informationread out of the IC device with use of a radio wave obtained from theresultant current including the current from the charging unit.

According to the ninth aspect of the present invention, the secondantenna allows to generate electric power and allows the charging unitto store the generated electric power. Therefore, the wirelesscommunication tag can stably communicate with the external reader/writerwith use of the sufficient amount of electric power. When a weak radiowave is received from the first antenna 8, a current is generated usingthe electric power stored in a capacitor by the second antenna 10.Therefore, an advantageous effect can be attained such that data readout of an internal memory unit inside the IC chip 14 can be transmittedthrough the first antenna 8 to the reader/writer 6, with use of the weakradio wave obtained from the resultant current including the currentfrom the capacitor 18, regardless of the low current obtained from thereceived weak radio wave. Furthermore, the electric power stored in thecapacitor 18 by the second antenna 10 is used only when the radio wavereceived from the first antenna 8 is weak, so that the IC chip 14 can beefficiently supplied with the high electric power.

A tenth aspect of the present invention is directed to a wirelesscommunication tag as set forth below. In the tenth aspect, the wirelesscommunication tag further a diode disposed between the IC device and thecharging unit, the diode for exercising ON/OFF control over the currentsupplied from the charging unit to the IC device, depending on intensityof the first radio wave received by the first antenna.

According to the tenth aspect of the present invention, the diodeexhibits a rectifying behavior, which allows the IC device to beefficiently supplied with the electric power stored in the chargingunit.

An eleventh aspect of the present invention is directed to a wirelesscommunication system, including: (a) a reader/writer for transmitting afirst radio wave including a reading-command signal; (b) a radio wavetransmitting device for transmitting a second electromotive radio wave;and (c) a wireless communication tag. The wireless communication tagincludes (i) an IC device for storing predetermined identificationinformation; (ii) a first antenna for receiving a first radio wave fromthe reader/writer, and for transmitting to the reader/writer thepredetermined identification information stored in the IC device readout by the command signal included in the first radio wave; (iii) asecond antenna for receiving a second radio wave from the radio wavetransmitting device; and (iv) a charging unit for storing electric powercaused by the second radio wave received from the second antenna. Thewireless communication tag, in the case where the first radio wavereceived from the first antenna is strong, activates the IC device witha current caused by the received strong first radio wave, and reads outthe predetermined identification information stored in the IC device, bythe command signal included in the first radio wave. The wirelesscommunication tag, in the case where the first radio wave received fromthe first antenna is weak, activates the IC device with a resultantcurrent of a current caused by the received weak first radio wave and acurrent from the charging unit previously storing the electric power,and reads out the predetermined identification information stored in theIC device, by the command signal included in the first radio wave. Thewireless communication tag transmits through the first antenna to thereader/writer, the predetermined identification information read out ofthe IC device with use of a radio wave obtained from the resultantcurrent including the current from the charging unit.

According to the eleventh aspect of the present invention, with use ofthe radio wave transmitted from the radio wave transmitting device, thesecond antenna allows to generate electric power and allows the chargingunit to store the caused electric power. Therefore, the wirelesscommunication tag can stably communicate with the external reader/writerwith use of the sufficient amount of electric power. When a weak radiowave is received from the first antenna 8, a current is generated usingthe electric power stored in a capacitor by the second antenna 10.Therefore, an advantageous effect can be attained such that data readout of an internal memory unit inside the IC chip 14 can be transmittedthrough the first antenna 8 to the reader/writer 6, with use of the weakradio wave obtained from the resultant current including the currentfrom the capacitor 18, regardless of the low current obtained from thereceived weak radio wave. Furthermore, the electric power stored in thecapacitor 18 by the second antenna 10 is used only when the radio wavereceived from the first antenna 8 is weak, so that the IC chip 14 can beefficiently supplied with the high electric power.

A twelfth aspect of the present invention is directed to a wirelesscommunication system as set forth below. In the twelfth aspect, thewireless communication system includes a diode disposed between the ICdevice and the charging unit, the diode for exercising ON/OFF controlover the current supplied from the charging unit to the IC device,depending on intensity of the first radio wave received by the firstantenna.

According to the twelfth aspect of the present invention, the diodeexhibits a rectifying behavior, which allows the IC device to beefficiently supplied with the electric power stored in the chargingunit.

The present invention can achieve a low-cost wireless communication tagand a wireless communication system, that ensure the sufficient amountof power charge regardless of a use environment to thereby increase acommunication distance with the reader/writer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side view showing a configuration of a wirelesscommunication tag according to one embodiment of the present invention;

FIG. 1B is a plan view showing the configuration of the wirelesscommunication tag shown in FIG. 1A;

FIG. 1C is a plan view showing a configuration of a wirelesscommunication tag according to another embodiment of the presentinvention;

FIG. 1D is a view showing a configuration of a wireless communicationsystem using the wireless communication tag of the present invention;and

FIG. 2 is a side view showing a configuration of an existing wirelesscommunication tag.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a wireless communication tag and a wireless communicationsystem, according to a first embodiment of the present invention, willbe described with reference to the accompanying drawings.

This embodiment assumes a wireless communication tag of the passivetype, in which electric power is generated by a radio wave. The wirelesscommunication tag 2, as shown in FIG. 1D, for example, stores (becomescharged with) electric power produced by an electromotive radio wave 4 etransmitted from a radio wave transmitting device 4. While the storedelectric power is employed as power supply, the wireless communicationtag 2 can read (or write) various types of data from (into) areader/writer 6 (actually, a communication antenna 6 t connected to thereader/writer 6).

A function required for the radio wave transmitting device 4 is only totransmit the electromotive radio wave 4 e with a frequency receivable bythe wireless communication tag 2. Thus, commercially availabletransmitting devices can be arbitrarily selectively applied to the radiowave transmitting device 4. In this case, a frequency of theelectromotive radio wave 4 e is set in response to a frequencyreceivable by a second antenna 10 of the wireless communication tag 2described later, and therefore, the frequency is not numerically limitedin particular. Furthermore, as the communication antenna 6 t, a UHFantenna with high communication accuracy (sensitivity, transmissiongain, or the like) may be applied, for example.

As shown in FIGS. 1A and 1B, at the wireless communication tag 2according to this embodiment, there are provided: a first antenna 8 forwirelessly communicating various types of data with the reader/writer 6(the communication antenna 6 t); the second antenna 10 for receiving theelectromotive radio wave 4 e transmitted from the radio wavetransmitting device 4 (FIG. 1D); and a transponder 12 (FIG. 1D) forexecuting operation of transmitting the data relating to thepredetermined identification information previously set in the wirelesscommunication tag 2 to the reader/writer 6 (FIG. 1D).

The transponder 12 has a function of relaying and transmitting thereceived data (electrical signal) or sending any of reply signals backbased on the abovementioned data (electrical signal). To perform thisfunction, the transponder 12 according to this embodiment has: acontroller for controlling data communicated (received) by the firstantenna 8; a charging unit for generating electric power by theelectromotive radio wave 4 e as well as for storing the thus generatedelectric power; and a memory unit for previously storing identificationinformation as well as for storing the data controlled by thecontroller.

The controller is provided with an IC chip 14. The IC chip 14 isconfigured as an integrated circuit which is integrated with constituentelements (not shown) such as a transistor, a diode, various types ofmemory units (such as a ROM and a RAM), and a resistor. In this case,various types of memory units of the controller may be applied or amemory element (not shown) such as a flash memory may be additionallyprovided in the wireless communication tag 2. Accordingly, theflexibility of a capacity design for storing the data relating to theidentification information (RFID) is increased to realize the wirelesscommunication tag 2 that is capable of communicating the largevolumetric data.

As the first antenna 8, the existing antenna (for example, a dipolarantenna or a loop antenna), that can wirelessly communicate with thereader/writer 6, may be arbitrarily applied depending on intended use oruse environment of the wireless communication tag 2. In this case, it ispreferable that an entire length (an antenna length) 8L of the firstantenna 8 be set to a half wavelength (λ/2) of data (a radio wave)communicated between the wireless communication tag 2 and thereader/writer 6. In this manner, a communication gain (transmissiongain) reaches its maximum value, thereby realizing efficient data (aradio wave) communication.

At the charging unit, a rectifying circuit 16 and a charging capacitor18, which serves as a secondary battery unit, are provided. Upon receiptof the electromotive radio wave 4 e from the second antenna 10, anelectromotive force rectified by the rectifying circuit 16 is stored inthe charging capacitor 18. In this case, the rectifying circuit 16includes various systems such as a half-wave rectification system and abridge rectification system. The half-wave rectification system can beconstructed of a single diode, whereas the bridge rectification systemis provided to rectify a current by using four diodes. For example, therectifying circuit 16 in this embodiment is formed as a bridge circuitwith the use of four diodes 16 d. In this manner, the wirelesscommunication tag 2 can be always supplied with a stable direct-currentvoltage (current). In addition to the charging capacitor 18, a lithiumbattery may be formed as the secondary battery unit as long as it isdesigned to store (become charged with) a voltage (current), oralternatively, the plurality of secondary battery units may be formed.

Furthermore, a diode 20 is intervened between the aforementionedcharging unit (the capacitor 18) and the controller (the IC chip 14).The diode 20 exercises ON/OFF control over a direct-current voltage(current) to be applied from the capacitor 18 to the IC chip 14 at thetime that the wireless communication tag reads (writes) various types ofdata through the wireless communication with the reader/writer 6 (thecommunication antenna 6 t) by activating the IC chip 14 by means of theelectric power (electric charge or electric energy) stored (charged) inthe capacitor 18.

A description will be given with respect to a case in which thecapacitor 18 is charged using the second antenna 10 in the wirelesscommunication tag 2 with the above-described structure. The secondantenna 10 always receives the electromotive radio wave 4 e for storingthe electric power in the capacitor 18. Hereinafter, a specificexplanation will be given.

When the second antenna 10 receives the electromotive radio wave 4 etransmitted from the radio wave transmitting device 4, thealternating-current voltage (current) is applied (output) to thetransponder 12 through the second antenna 10. The electromotive radiowave 4 e is defined herein as an electromagnetic wave that is propagatedwhile an electric field and a magnetic field are alternately generated.When an alternating magnetic field acts on the second antenna 10, thealternating-current voltage (electric current) that has been convertedthrough the second antenna 10 is applied (output) to the transponder 12.

At this time, the alternating-current voltage (current) applied (output)to the transponder 12 is converted into direct voltage (current) throughthe two upper diodes 16 d of the rectifying circuit 16, and thereafter,the thus converted direct voltage is stored (charged) in the capacitor18. The direct voltage is continuously stored (charged) while the secondantenna 10 of the wireless communication tag 2 receives theelectromotive radio wave 4 e transmitted from the radio wavetransmitting device 4. Accordingly, the capacitor 18 of the wirelesscommunication tag 2 is kept in a fully charged condition at all times.As described above, the electric power stored in the capacitor 18through the antenna 10 is used to activate the IC chip 14 as well as togenerate a strong radio wave to be transmitted from the first antenna 8to the reader/writer 6, when the first antenna 8 receives a weak radiowave from the reader/writer 6, as described later.

Next, a description will be given with respect to the wirelesscommunication tag 2 according to this embodiment in the case where aradio wave that the first antenna 8 receives from the communicationantenna 6 t of the reader/writer 6 is strong and the case where theradio wave is weak. In the wireless communication tag 2, upon readingdata relating to the identification information out of an internalmemory unit of the IC chip 14, the reader/writer 6 transmits the radiowave including the command signal to the first antenna 8 through thecommunication antenna 6 t.

First, a case in which the first antenna 8 receives a strong radio wavewill be explained. When a radio wave that the first antenna 8 receivesis strong, this radio wave generates electric power, and thus, a currentflows into the IC chip 14. The IC chip 14 is activated by this current,whereas the data relating to the identification information (such as anidentification code peculiar to the tag and information relating to ause environment of the tag) stored in the internal memory unit of the ICchip 14 is read out by a command signal included in the radio wave. Theread-out data is transmitted from the first antenna 8 to thereader/writer 6 with use of the strong radio wave obtained from thegenerated current described above. Specifically, when the radio wavethat the first antenna 8 receives is strong, the data is read out of theIC chip 14 and transmitted to the reader/writer 6 only with use of thecurrent obtained from the radio wave received by the first antenna,without consuming the electric power of the capacitor 18 storing theelectric charge by the electromotive radio wave 4 e received from thesecond antenna 10. In the case where the first antenna 8 receives thestrong radio wave, a voltage at a side of the first antenna 8 increases,so that current does not flow from the diode 20 to the IC chip 14 byusing the electric charge of the capacitor 18 resulting from therectifying behavior of the diode 20 achieved by a reverse bias.

Next, such a case is explained, that the first antenna 8 receives a weakradio wave. When the radio wave that the first antenna 8 receives isweak, the voltage at the side of the first antenna 8 decreases, so thatthe current flows from the diode 20 to the IC chip 14 by using theelectric charge of the capacitor 18 resulting from the rectifyingbehavior of the diode 20 achieved by a reverse bias. In this case, thecurrent for activating the IC chip 14 is a resultant current of acurrent from the capacitor 18 storing the electric charge and a currentobtained from the weak radio wave received from the first antenna 8. TheIC chip 14 is activated by this resultant current whereas the datarelating to the identification information stored in the internal memoryunit of the IC chip 14 is read out by the command signal included in theradio wave. The read-out data is transmitted from the first antenna 8 tothe reader/writer 6 with the strong radio wave obtained from theaforementioned resultant current. Specifically, in the case where theradio wave that the first antenna 8 receives is weak, the data is readout of the IC chip 14 and transmitted to the reader/writer 6 with use ofthe electric power stored in the capacitor 18 by the second antenna 10.

As described above, the wireless communication tag 2 according to thisembodiment generates the current using the electric power previouslystored in the capacitor 18 by the second antenna 10, in the case ofreceipt of the weak radio wave from the first antenna 8. Therefore, thiswireless communication tag 2 can attain such an advantageous effect thatthe data read out of the internal memory unit of the IC chip 14 can betransmitted to the reader/writer 6 through the first antenna 8, with useof the strong radio wave obtained from the resultant current includingthe current from the capacitor 18, regardless of the low currentobtained from the aforementioned received weak radio wave. Furthermore,the electric power stored in the capacitor 18 by the second antenna 10is used only when the radio wave that the first antenna 8 receives isweak, so that the IC chip 14 can be sufficiently supplied with the highelectric power.

According to this embodiment, the charging unit (the capacitor 18) canefficiency store (become charged with) electric power in a short periodof time, and thus, can be kept in a fully charged condition regardlessof environment of using the wireless communication tag 2 because thesecond antenna 10 that receives the electromotive radio wave 4 e forcharging the charging unit is formed separately from the first antenna 8that wirelessly communicates the predetermined data (the readout radiowave, for example) with the reader/writer 6. In this manner, whenproviding the reader/writer 6 with the data relating to theidentification information, use of the electric power (electric chargeor electric energy) in a fully charged condition enables the wirelesscommunication tag 2 to perform steady telecommunication at all times.

According to this embodiment, furthermore, the charging unit (thecapacitor 18) can be always maintained in a fully charged state, thusmaking it possible to always maintain an output of the data transmissionto its required maximum, when the data relating to the identificationinformation is supplied to the reader/writer 6. In this manner, acommunication distance Ld (FIG. 1D) between the wireless communicationtag 2 and the reader/writer 6 (specifically, the communication antenna 6t connected to the reader/writer 6) can be increased more significantlyin comparison with that of the related art.

According to this embodiment, yet furthermore, the data can beefficiently transmitted and received by forming the second antenna 10designed exclusively for receipt of the electromotive radio wave 4 e forcharging the charging unit, separately from the first antenna 8 designedexclusively for reception of the data (the readout radio wave). In thiscase, it is preferable that a radio wave frequency (for example, a UHFband (band between 860 and 960 MHz) at the time of communication betweenthe first antenna 8 and the reader/writer 6, and a frequency (forexample, a band of 13.56 MHz or 2.45 GHz) of the electromotive radiowave 4 e received from the second antenna 10 be set to be different fromeach other.

With the above setting, the frequency accuracy, stability, andmodulation or the like, of the electromotive radio wave 4 e received bythe second antenna 10 can be set completely independently from the radiowave transmitted from the reader/writer 6 and received by the firstantenna 8. In this manner, the first and second antennas 8, 10 can beprevented from interfering with each other in the case of using radiowaves of the same frequency. At the same time, an output frequency ofthe electromotive radio wave 4 e, for example, can be set within afrequency band in which the radio wave output is under loose regulation.As a result, the electromotive radio wave 4 e is transmitted oncondition that an output thereof is increased, so that the wirelesscommunication tag 2 can be improved in electromotive efficiency andcharging efficiency. In the case where a frequency band, which isavailable for use in communication, is limited, the frequency band,which is actually available, becomes narrower because the frequencybands at both ends are set to guard bands for preventing interferencewith adjacent frequency bands. Therefore, a great advantage is attainedby the fact that the output frequency of the electromotive radio wave 4e can be set within a frequency band in which the radio wave output isloosely regulated.

According to this embodiment, furthermore, the electromotive radio wave4 e for charging the charging unit of the wireless communication tag 2is not used to read out the data relating to the identificationinformation stored in the IC chip 14, thus making it completelyunnecessary to consider the frequency accuracy, stability, modulation orthe like, of the electromotive radio wave 4 e. Therefore, the radio wavetransmitting device 4 for transmitting the electromotive radio wave 4 ecan be made up of a simple transmitting device and antenna only, thusallowing the device to be produced at very low cost. Accordingly, thewireless communication system (FIG. 1D) having the radio wavetransmitting device 4, the wireless communication tag 2, and thereader/writer 6 (the communication antenna 6 t) can be readily realizedat low cost.

In the wireless communication system as described above, it is possibleto ensure the sufficient amount of electric power for driving thewireless communication tag 2 from the charging unit over a long periodof time, even in location with a low electric field intensity or under apoor radio-wave condition. Thus, the data relating to the identificationinformation can be stably transmitted and received, whereastelecommunication can be realized.

As the second antenna 10 according to the embodiment described above(the wireless communication tag 2 and the wireless communicationsystem), furthermore, the existing antenna (such as a dipolar antenna ora loop antenna) that can wirelessly communicate with the radio wavetransmitting device 4 may be arbitrarily applied depending on intendeduse or use environment of the wireless communication tag. With respectto the second antenna 10, it is preferable that an entire length (anantenna length) 10L (FIG. 1B) thereof be set to a half wavelength (λ/2)of the data (the radio wave) communicated between the wirelesscommunication tag 2 and the radio transmitting device 4. In this manner,the communication gain (transmission gain) reaches its maximum value,thereby realizing the efficient data (radio wave) communication.

In this case, the antenna length 10L of the second antenna 10 can bearbitrarily (freely) set regardless of the antenna length of the firstantenna 8 as described above, and thus, it is not numerically limited inparticular.

In the foregoing embodiment, various types of data (such as the datarelating to the identification information) stored in the memory of theIC chip 14 may be arranged to be wirelessly transmitted and receivedbetween the second antenna 10 and the reader/writer 6.

While the foregoing embodiment assumedly described that the dipolarantenna or the loop antenna is used as the second antenna 10 of thewireless communication tag 2, instead of these antennas, a resonantcircuit may be used to construct the second antenna 10, as shown in FIG.1C.

When the electromotive radio wave 4 e transmitted from the radio wavetransmitting device is applied, the above resonant circuit generates anatural oscillation, and then, resonates, whereby the electric power(the electric charge or the electric energy) is stored (charged) in thecapacitor 18 through the rectifying circuit 16. While the thus generatedelectric power is employed as power supply, the identificationinformation can be read through the wireless communication of the datawith the reader/writer 6 in a manner similar to that in the abovedescribed embodiment. In this manner, provision of the simplyconstructible resonant circuit allows the wireless communication tag tointernally generate the electric power, thus achieving low-costproduction and ensuring the sufficient amount of power charge regardlessof the use environment. The resonant circuit may be installed in plural.Installing the plurality of resonant circuits in this manner allows thesingle wireless communication tag 2 to be used with a plurality offrequency bands. For example, it becomes possible to construct oneresonant circuit with a UHF band and the other resonant circuit with a13.56 MHz band (or 2.45 GHz band). Therefore, frequencies can be used incombination or selectively used depending on each of the intended usesor location described later. Furthermore, the amount of electric powergenerated by each of the resonant circuits is increased by providing theplurality of resonant circuits, so that electric power can be stored(charged), thus making it possible to cover the required amount ofelectric power due to upsizing of the wireless communication tag 2.

The second antenna 10 and the resonant circuit may be constructed foruse in combination (not shown). In this case, with the electric powerreceived by the second antenna 10 and the electric power generated inthe resonant circuit, lower-cost production can be achieved and thesufficient amount of power charge can be ensured regardless of the useenvironment.

While, in the wireless communication tag 2 according to the foregoingembodiment, the data relating to the identification information read outof the internal memory unit of the IC chip 14 is transmitted from thefirst antenna 8 to the reader/writer 6, this invention is not limitativethereto. For example, the data relating to the identificationinformation may be transmitted from the second antenna 10 to thereader/writer 6. In this case, when the IC chip 14 is activated with thepredetermined current described above, the predetermined current flowsthrough the two lower-side diodes 16 d of the rectifying circuit 16 tothe second antenna 10. Furthermore, in the case where the radio wavefrom the second antenna 10 is received at the side of the reader/writer6, it is preferable that the reader/writer 6 include a receiving antennawhich covers a frequency band of the second antenna 10, in addition tothe communication antenna 6 t designed for communication with the firstantenna 8.

While, in the foregoing embodiment, intended use of the wirelesscommunication tag 2 was not particularly mentioned, the wirelesscommunication tag 2 is applicable to a variety of intended uses such asa distribution use, a history management use, and a presence managementuse. In the distribution use, the wireless communication tag 2 isaffixed to products at the stage of production at a factory to therebykeep track of transportation of the products through a subsequentdelivery route. In the history management use, the wirelesscommunication tag 2 is used to record history information relevant to:through which route the product was passed; how it was processed; towhich it was delivered; and the like in a distribution process of theproduct. In the presence management use, the wireless communication tag2 is used to manage presence information relevant to a current locationindicating where a target person is now.

1. A wireless communication tag previously set with predeterminedidentification information, the wireless communication tag comprising:(i) a first antenna for wirelessly communicating various types of databetween a reader/writer and an IC device; (ii) a controller forcontrolling the data communicated through the first antenna; (iii) asecond antenna for receiving an electromotive radio wave for generatingelectric power from an electromotive radio wave; and (iv) a chargingunit for generating electric power from the electromotive radio wavereceived by the second antenna as well as for storing the generatedelectric power, wherein: the electric power stored in the charging unitis used, thereby allowing either one of the first and second antennas toprovide, to the reader/writer, data relating to the identificationinformation, the wireless communication tag further comprises a diodedisposed between the IC device and the charging unit, and the diodeexercises ON/OFF control of direct current voltage that is applied fromthe charging unit to the IC device, in order to activate the IC deviceby means of electric power generated and stored by the charging unit,when a radio wave that is received by the first antenna is weak.
 2. Thewireless communication tag according to claim 1, wherein: the secondantenna wirelessly transmits the identification data to thereader/writer when the first antenna wirelessly receives theidentification data from the reader/writer.
 3. The wirelesscommunication tag according to claim 1, wherein: a radio wave frequencyat the time of communication between the first antenna and thereader/writer and a frequency of the electromotive radio wave receivedfrom the second antenna are set different from each other.
 4. Thewireless communication tag according to claim 1, wherein: a memory unitfor previously storing the identification information as well as forstoring the data controlled by the controller.
 5. The wirelesscommunication tag according to claim 1, wherein: the charging unitincludes a rectifying circuit and a secondary battery unit; and thesecondary battery unit stores an electromotive force rectified by therectifying circuit upon receipt of the electromotive radio wave from thesecond antenna.
 6. The wireless communication tag according to claim 5,wherein: the rectifying circuit is formed as a bridge circuit.
 7. Thewireless communication tag according to claim 1, further comprising aresonant circuit.
 8. The wireless communication tag according to claim1, wherein: the second antenna is configured of a resonant circuit.
 9. Awireless communication tag, comprising: (i) an IC device for storingpredetermined identification information; (ii) a first antenna forreceiving, from an external reader/writer, a first radio wave includinga reading-command signal and for transmitting, to the externalreader/writer, the predetermined identification information stored inthe IC device and read out by the reading-command signal; (iii) a secondantenna for receiving a second electromotive radio wave from an externalpredetermined device; and (iv) a charging unit for storing electricpower generated from the second radio wave received by the secondantenna, wherein: in the case where the first radio wave received by thefirst antenna is strong, the wireless communication tag activates the ICdevice with a current caused by the received strong first radio wave andreads out the predetermined identification information stored in the ICdevice in response to the command signal included in the first radiowave; in the case where the first radio wave received from the firstantenna is weak, the wireless communication tag activates the IC devicewith a resultant current of a current caused by the received weak firstradio wave and a current from the charging unit previously storing theelectric power and reads out the predetermined identificationinformation stored in the IC device in response to the command signalincluded in the first radio wave; the wireless communication tagtransmits, through the first antenna to the external reader/writer, thepredetermined identification information read out of the IC device withuse of a radio wave obtained from the resultant current including thecurrent from the charging unit; the wireless communication tag furthercomprises a diode that is disposed between the IC device and thecharging unit; and the diode exercises ON/OFF control of a directcurrent voltage that is applied from the charging unit to the IC devicein order to activate the IC device by means of electric power generatedand stored by the charging unit when a radio wave that is received bythe first antenna is weak.
 10. A wireless communication system,comprising: (a) a reader/writer for transmitting a first radio waveincluding a reading-command signal; (b) a radio wave transmitting devicefor transmitting a second, electromotive radio wave; and (c) a wirelesscommunication tag including: (i) an IC device for storing predeterminedidentification information; (ii) a first antenna for receiving a firstradio wave from the reader/writer and for transmitting to thereader/writer the predetermined identification information stored in theIC device read out in response to the command signal included in thefirst radio wave; (iii) a second antenna for receiving a second radiowave from the radio wave transmitting device; and (iv) a charging unitfor storing electric power generated from the second radio wave receivedfrom the second antenna, wherein: in the case where the first radio wavereceived from the first antenna is strong, the wireless communicationtag activates the IC device with a current caused by the received strongfirst radio wave and reads out the predetermined identificationinformation stored in the IC device in response to the command signalincluded in the first radio wave; in the case where the first radio wavereceived from the first antenna is weak, the wireless communication tagactivates the IC device with a resultant current of a current caused bythe received weak first radio wave and a current from the charging unitpreviously storing the electric power and reads out the predeterminedidentification information stored in the IC device in response to thecommand signal included in the first radio wave; the wirelesscommunication tag transmits, through the first antenna to thereader/writer, the predetermined identification information read out ofthe IC device with use of a radio wave obtained from the resultantcurrent including the current from the charging unit; the wirelesscommunication tag further comprises a diode that is disposed between theIC device and the charging unit; and the diode exercises ON/OFF controlof a direct current voltage that is applied from the charging unit tothe IC device in order to activate the IC device by means of electricpower generated and stored by the charging unit when a radio wave thatis received from the first antenna is weak.
 11. A wireless communicationtag, comprising: (i) an IC device for storing predeterminedidentification information; (ii) an antenna for receiving a first radiowave which is inclusive of a command signal from a reader/writer, inorder to transmit the predetermined identification information stored inthe IC device to the reader/writer, and for receiving a second,electromotive radio wave from an external predetermined device; (iii) acharging unit for generating electric power from the second radio wavereceived from the antenna and for storing the generated electric power;and (iv) a current control unit which is disposed between the IC deviceand the charging unit for exercising ON/OFF control of a current to besupplied from the charging unit to the IC device in accordance with anintensity of the first radio wave received by the antenna, wherein thecurrent control unit exercises ON/OFF control of a current 1) to readout the predetermined identification information stored in the IC devicewith use of an electromotive force obtained by the received first radiowave when the first radio wave received from the antenna is strong; and2) to read out the predetermined identification information stored inthe IC device with use of electric power stored in the charging unitwhen the first radio wave received from the antenna is weak, theelectric power stored in the charging unit having been generated byreception of the second radio wave.